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Abstract:

According to one embodiment, a magnetic head for perpendicular recording
includes a first magnetic core includes a main pole configured to produce
a recording magnetic field, and a return pole configured to reflux
magnetic flux from the main pole to form a magnetic circuit in
conjunction with the main pole, a first coil configured to excite
magnetic flux in the magnetic circuit, side shields arranged individually
on opposite sides of the main pole transversely relative to a track so as
to be magnetically separated from the main pole and formed integrally
with the return pole, a second magnetic core configured to form a
physically closed magnetic path, a part of which comprises the return
pole, and a second coil wound around the second magnetic core and
configured to excite magnetic flux in the closed magnetic path.

Claims:

1. A magnetic head for perpendicular recording configured to record data
in a recording medium which comprises a recording layer with a magnetic
anisotropy perpendicular to a surface of the medium, comprising: a first
magnetic core comprising a main pole, which comprises a distal end
portion opposed to the recording medium and is configured to produce a
recording magnetic field, and a return pole opposed to a trailing side of
the main pole with a write gap therebetween and configured to reflux
magnetic flux from the main pole to form a magnetic circuit in
conjunction with the main pole; a first coil configured to excite
magnetic flux in the magnetic circuit comprising the main pole and the
return pole; side shields arranged individually on opposite sides of the
main pole transversely relative to a track so as to be magnetically
separated from the main pole and formed integrally with the return pole;
a second magnetic core configured to form a physically closed magnetic
path, a part of which comprises the return pole; and a second coil wound
around the second magnetic core and configured to excite magnetic flux in
the closed magnetic path comprising the second magnetic core.

2. The magnetic head of claim 1, wherein the second magnetic core
comprises a first magnetic pole on a leading side of the main pole and
comprising first yoke portions connected individually to the side
shields, a second magnetic pole on a leading side of the first magnetic
pole and comprising second yoke portions connected individually to the
side shields, and a junction connecting the first and second magnetic
poles.

3. The magnetic head of claim 2, wherein the side shields extend beyond
the main pole to the leading side.

4. The magnetic head of claim 3, wherein the side shields are connected
to each other on the leading side of the main pole.

5. The magnetic head of claim 4, wherein the first yoke portions of the
first magnetic pole and the second yoke portions of the second magnetic
pole are connected to a junction for the side shields.

6. A disk drive comprising: a recording medium comprising a recording
layer with a magnetic anisotropy perpendicular to a surface of the
medium; a drive section configured to rotate the recording medium; and a
magnetic head comprising a slider having a facing surface opposed to a
surface of the recording medium and a head section on the slider and
configured to perform data processing on the recording medium, the head
section comprising: a first magnetic core comprising a main pole, which
comprises a distal end portion opposed to the recording medium and is
configured to produce a recording magnetic field, and a return pole
opposed to the trailing side of the main pole with a write gap
therebetween and configured to reflux magnetic flux from the main pole to
form a magnetic circuit in conjunction with the main pole, a first coil
configured to excite magnetic flux in the magnetic circuit comprising the
main pole and the return pole, side shields arranged individually on
opposite sides of the main pole transversely relative to a track so as to
be magnetically separated from the main pole and formed integrally with
the return pole, a second magnetic core configured to form a physically
closed magnetic path, a part of which comprises the return pole, and a
second coil wound around the second magnetic core and configured to
excite magnetic flux in the closed magnetic path comprising the second
magnetic core.

7. The disk drive of claim 6, wherein the second magnetic core comprises
a first magnetic pole on a leading side of the main pole and comprising
first yoke portions connected individually to the side shields, a second
magnetic pole on a leading side of the first magnetic pole and comprising
second yoke portions connected individually to the side shields, and a
junction connecting the first and second magnetic poles.

8. The disk drive of claim 7, further comprising a head controller
configured to control a magnitude of a current supplied to the second
coil for obtaining a minimum feasible track pitch, based on the current
supplied to the second coil and an error rate.

9. The disk drive of claim 8, wherein the head controller comprises a
first current controller configured to control a current supplied to the
first coil, a second current controller configured to control the current
supplied to the second coil, an error-rate measurement section configured
to measure the error rate, and a data operation unit configured to
calculate a current with which a minimum feasible track pitch to reduce
the error rate is obtained, based on currents supplied from the first and
second current controllers and the error rate measured by the error-rate
measurement section.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2010-079073, filed Mar. 30, 2010;
the entire contents of which are incorporated herein by reference.

FIELD

[0002] Embodiments described herein relate generally to a magnetic head
for perpendicular magnetic recording used in a disk drive and the disk
drive provided with the head.

BACKGROUND

[0003] A disk drive, such as a magnetic disk drive, comprises a magnetic
disk, spindle motor, magnetic head, and carriage assembly. The magnetic
disk is disposed in a base. The spindle motor supports and rotates the
disk. The magnetic head reads and writes data from and to the disk. The
carriage assembly supports the head for movement relative to the disk.
The carriage assembly comprises a rotatably supported arm and a
suspension extending from the arm, and the magnetic head is supported on
an extended end of the suspension. The head comprises a slider mounted on
the suspension and a head section disposed on the slider. The head
section comprises a recording element for writing and a reproduction
element for reading.

[0004] Magnetic heads for perpendicular magnetic recording have recently
been proposed in order to increase the recording density and capacity of
a magnetic disk drive or reduce its size. In one such magnetic head, a
recording head comprises a main pole configured to produce a
perpendicular magnetic field, return or write/shield pole, and coil. The
return pole is located on the trailing side of the main pole with a write
gap therebetween and configured to close a magnetic path that leads to a
magnetic disk. The coil serves to pass magnetic flux through the main
pole.

[0005] In recording a record pattern along a track of the magnetic disk,
recording magnetic fields also simultaneously leak from the opposite
sides of the main pole transversely relative to the track. There is
provided a head that comprises side shields arranged individually on the
opposite sides of the main pole transversely relative to the track,
whereby the leakage magnetic fields are reduced.

[0006] In recording data in a perpendicular recording medium by means of
the magnetic head for perpendicular recording constructed in this manner,
a substantially perpendicular magnetic field is formed on a surface of
the medium just below the main pole. This magnetic field returns to the
return pole through a soft magnetic layer below a recording layer of the
perpendicular recording medium. However, a certain region just below the
return pole includes an area on which magnetic fields are concentrated.
In some cases, the concentrated magnetic fields may destabilize
magnetization of the recording layer and erase or degrade recorded data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A general architecture that implements the various feature of the
embodiments will now be described with reference to the drawings. The
drawings and the associated descriptions are provided to illustrate the
embodiments and not to limit the scope of the invention.

[0008] FIG. 1 is an exemplary perspective view showing an HDD according to
a first embodiment;

[0009] FIG. 2 is an exemplary side view showing a magnetic head and
suspension of the HDD;

[0010] FIG. 3 is an exemplary enlarged sectional view showing a head
section of the magnetic head;

[0011] FIG. 4 is an exemplary exploded perspective view schematically
showing a recording head of the magnetic head;

[0012] FIG. 5 is an exemplary perspective view schematically showing the
recording head of the magnetic head;

[0013] FIG. 6 is an exemplary front view of a disk-side end portion of the
recording head taken from the side of a main pole;

[0014] FIG. 7 is an exemplary plan view of the recording head section
taken from the side of an ABS of a slider;

[0015] FIG. 8 is an exemplary block diagram showing a control section of
the magnetic head of the HDD;

[0016] FIG. 9 is an exemplary diagram showing the relationship between the
track pitch and error rate for each of supplied currents;

[0017] FIG. 10 is an exemplary diagram showing the relationship between
each supplied current and a minimum feasible track pitch;

[0018] FIG. 11 is an exemplary diagram comparatively showing transverse
distributions (relative to the track) of magnetic flux produced just
below the main pole for each of the magnetic head of the first embodiment
and a magnetic head according to a comparative example;

[0020] FIG. 13 is an exemplary diagram showing the relationship between
the error rate and a head position transversely relative to the track for
each of the magnetic heads according to the first embodiment and
comparative example;

[0021] FIG. 14 is an exemplary exploded perspective view schematically
showing a recording head of a magnetic head of an HDD according to a
second embodiment;

[0022] FIG. 15 is an exemplary enlarged sectional view showing the
recording head of the magnetic head of the second embodiment; and

[0023] FIG. 16 is an exemplary plan view of the recording head of the
magnetic head of the second embodiment taken from the side of an ABS.

DETAILED DESCRIPTION

[0024] Various embodiments will be described hereinafter with reference to
the accompanying drawings.

[0025] In general, according to one embodiment, a magnetic head for
perpendicular recording is configured to record data in a recording
medium which comprises a recording layer with a magnetic anisotropy
perpendicular to a surface of the medium. The magnetic head comprises: a
first magnetic core comprising a main pole, which comprises a distal end
portion opposed to the recording medium and is configured to produce a
recording magnetic field, and a return pole opposed to a trailing side of
the main pole with a write gap therebetween and configured to reflux
magnetic flux from the main pole to form a magnetic circuit in
conjunction with the main pole; a first coil configured to excite
magnetic flux in the magnetic circuit comprising the main pole and the
return pole; side shields arranged individually on opposite sides of the
main pole transversely relative to a track so as to be magnetically
separated from the main pole and formed integrally with the return pole;
a second magnetic core configured to form a physically closed magnetic
path, a part of which comprises the return pole; and a second coil wound
around the second magnetic core and configured to excite magnetic flux in
the closed magnetic path comprising the second magnetic core.

[0026] A first embodiment in which a disk drive is applied to a hard disk
drive (HDD) will now be described in detail with reference to the
accompanying drawings.

[0027] FIG. 1 shows the internal structure of the HDD with its top cover
removed, and FIG. 2 shows a flying magnetic head. As shown in FIG. 1, the
HDD comprises a case 10, which comprises a base 11 in the form of an
open-topped rectangular box and a top cover (not shown) in the form of a
rectangular plate. The top cover is attached to the base by screws so as
to close the top opening of the base. Thus, the case 10 is kept airtight
inside and can communicate with the outside through a breather filter 26
only. The base 11 and the top cover are formed of a metallic material
such as aluminum, iron, stainless steel, or cold-rolled carbon steel.

[0028] The base 11 carries thereon a magnetic disk 12, for use as a
recording medium, and a mechanical unit. The mechanical unit comprises a
spindle motor 13, a plurality (e.g., two) of magnetic heads 33, head
actuator 14, and voice coil motor (VCM) 15. The spindle motor 13 supports
and rotates the magnetic disk 12. The magnetic heads 33 record and
reproduce data in and from the disk 12. The head actuator 14 supports the
heads 33 for movement relative to the disk 12. The VCM 15 pivots and
positions the head actuator. The base 11 further carries a ramp load
mechanism 18, inertial latch mechanism 20, and board unit 17. The ramp
load mechanism 18 holds the magnetic heads 33 in positions off the
magnetic disk 12 when the heads are moved to the outermost periphery of
the disk. The inertial latch mechanism 20 holds the head actuator 14 in a
retracted position if the HDD is jolted, for example. Electronic
components, such as a preamplifier, head IC, etc., are mounted on the
board unit 17.

[0029] A printed circuit board 25 that constitutes a control section is
attached to the outer surface of a bottom wall of the base 11 by screws
so as to face the bottom wall of the base. The circuit board 25 controls
the operations of the spindle motor 13, VCM 15, and magnetic heads 33
through the board unit 17.

[0030] As shown in FIGS. 1 and 2, the magnetic disk 12 is a perpendicular
two-layer film medium. The disk 12 comprises a substrate 16 formed of a
nonmagnetic disk with a diameter of, for example, about 2.5 inches. A
soft magnetic layer 23 called a soft magnetic underlayer is formed on
each surface of the substrate 16. The soft magnetic layer 23 is overlaid
by a perpendicular magnetic recording layer 22, which has a magnetic
anisotropy perpendicular to the disk surface. Further, a protective film
is formed on the recording layer 22.

[0031] As shown in FIG. 1, the magnetic disk 12 is coaxially fitted on the
hub of the spindle motor 13 and clamped and secured to the hub by a clamp
spring 21, which is attached to the upper end of the hub by screws. The
disk 12 is rotated at a predetermined speed in the direction of arrow B
by the spindle motor 13.

[0032] The head actuator 14 comprises a bearing 24 secured to the bottom
wall of the base 11 and a plurality of arms 27 extending from the
bearing. The arms 27 are arranged parallel to the surfaces of the
magnetic disk 12 and at predetermined intervals and extend in the same
direction from the bearing 24. The head actuator 14 comprises elastically
deformable suspensions 30 each in the form of an elongated plate. Each
suspension 30 is formed of a plate spring, the proximal end of which is
secured to the distal end of its corresponding arm 27 by spot welding or
adhesive bonding and which extends from the arm. Each suspension 30 may
be formed integrally with its corresponding arm 27. The magnetic heads 33
are supported individually on the respective extended ends of the
suspensions 30. Each arm 27 and its corresponding suspension 30
constitute a head suspension, and the head suspension and each magnetic
head 33 constitute a head suspension assembly.

[0033] As shown in FIG. 2, each magnetic head 33 comprises a substantially
cuboid slider 42 and read/write head section 44 on an outflow end
(trailing end) of the slider. Each head 33 is secured to a gimbal spring
41 on the distal end portion of each corresponding suspension 30. A head
load L directed to the surface of the magnetic disk 12 is applied to each
head 33 by the elasticity of the suspension 30. The two arms 27 are
arranged parallel to and spaced apart from each other, and the
suspensions 30 and heads 33 mounted on these arms face one another with
the magnetic disk 12 between them.

[0034] Each magnetic head 33 is electrically connected to a main flexible
printed circuit (FPC) board 38 (described later), through the suspension
30 and a relay FPC 35 on the arm 27.

[0035] As shown in FIG. 1, the board unit 17 comprises an FPC main body 36
formed of a flexible printed circuit board and the main FPC 38 extending
from the FPC main body. The FPC main body 36 is secured to the bottom
surface of the base 11. The electronic components, including a
preamplifier and head IC 37, are mounted on the FPC main body 36. An
extended end of the main FPC 38 is connected to the head actuator 14 and
also connected to each magnetic head 33 through each relay FPC 35.

[0036] The VCM 15 comprises a support frame (not shown) extending from the
bearing 24 in the direction opposite to the arms 27 and a voice coil
supported on the support frame. When the head actuator 14 is assembled to
the base 11, the voice coil is located between a pair of yokes 34 that
are secured to the base 11. Thus, the voice coil, along with the yokes
and a magnet secured to the yokes, constitutes the VCM 15.

[0037] If the voice coil of the VCM 15 is energized with the magnetic disk
12 rotating, the head actuator 14 pivots, whereupon each magnetic head 33
is moved to and positioned on a desired track of the magnetic disk 12. As
this is done, the head 33 is moved radially relative to the disk 12
between the inner and outer peripheral edges of the disk.

[0038] The following is a detailed description of a configuration of each
magnetic head 33. FIG. 3 is an exemplary enlarged sectional view showing
the head section 44 of the head 33.

[0039] As shown in FIGS. 2 and 3, each magnetic head 33 is formed as a
flying head, and comprises the substantially cuboid slider 42 and the
head section 44 formed on the outflow or trailing end of the slider. The
slider 42 is formed of, for example, a sintered body (AlTic) containing
alumina and titanium carbide, and the head section 44 is a thin film.

[0040] The slider 42 has a rectangular disk-facing surface or air-bearing
surface (ABS) 43 configured to face a surface of the magnetic disk 12.
The slider 42 is caused to fly by airflow C that is produced between the
disk surface and the ABS 43 as the magnetic disk 12 rotates. The
direction of airflow C is coincident with a direction of rotation B of
the disk 12. The slider 42 is located on the surface of the disk 12 in
such a manner that the longitudinal direction of the ABS 43 is
substantially coincident with the direction of airflow C.

[0041] The slider 42 comprises leading and trailing ends 42a and 42b on
the inflow and outflow sides, respectively, of airflow C. The ABS 43 of
the slider 42 is formed with leading and trailing steps, side steps,
negative-pressure cavity, etc., which are not shown.

[0042] As shown in FIG. 3, the head section 44 is formed as a dual-element
magnetic head, comprising a reproduction head 54 and recording head 56
formed on the trailing end 42b of the slider 42 by thin-film processing.

[0043] The reproduction head 54 comprises a magnetic film 63 having a
magnetoresistive effect and shield films 62a and 62b located on the
trailing and leading sides, respectively, of the magnetic film 63 so as
to sandwich the magnetic film between them. The respective lower ends of
the magnetic film 63 and shield films 62a and 62b are exposed in the ABS
43 of the slider 42.

[0044] The recording head 56 is located nearer to the trailing end 42b of
the slider 42 than the reproduction head 54. FIG. 4 is an exemplary
exploded perspective view schematically showing the recording head 56,
and FIG. 5 is an exemplary perspective view schematically showing the
recording head 56 and magnetic disk 12. FIG. 6 is an exemplary front view
of a disk-side end portion of the recording head taken from the side of a
main pole, and FIG. 7 is an exemplary plan view of the recording head
section taken from the side of the ABS 43 of the slider 42.

[0045] As shown in FIGS. 3 to 5, the recording head 56 comprises first and
second magnetic cores 56a and 56b. The first magnetic core 56a comprises
a main pole 66, return pole (write/shield electrode) 68, junction 67, and
recording coil (first coil) 71. The main pole 66 is formed of a
high-permeability material and produces a recording magnetic field
perpendicular to the surfaces of the magnetic disk 12. The return pole 68
is located on the trailing side of the main pole 66 serves to efficiently
close a magnetic path through the soft magnetic layer 23 just below the
main pole. The junction 67 connects respective upper parts of the main
and return poles 66 and 68. The recording coil 71 is located so as to
wind around a magnetic path including the main and return poles 66 and 68
to pass magnetic flux to the main pole 66 while a signal is being written
to the magnetic disk 12.

[0046] As shown in FIGS. 3 to 6, the main pole 66 extends substantially at
right angles to the surfaces of the magnetic disk 12. A distal end
portion 66a of the main pole 66 on the side of the magnetic disk 12 is
tapered toward the disk surface. As shown in FIG. 7, the distal end
portion 66a of the main pole 66 is formed with, for example, a
trapezoidal cross-section and comprises a trailing end face 67a, leading
end face 67b, and opposite side faces 67c. The trailing end face 67a has
a predetermined width and is located on the trailing end side. The
leading end face 67b, which is narrower than the trailing end face 67a,
is opposed to the trailing end face. The distal end face of the main pole
66 is exposed in the ABS 43 of the slider 42. The trailing end face 67a
is almost as wide as a track of the magnetic disk 12.

[0047] As shown in FIGS. 3 to 7, the return pole 68 is substantially
L-shaped and its distal end portion 68a has an elongated rectangular
shape. The distal end face of the return pole 68 is exposed in the ABS 43
of the slider 42. A leading end face 68b of the distal end portion 68a
extends transversely relative to the track of the magnetic disk 12. The
leading end face 68b is opposed parallel to the trailing end face 67a of
the main pole 66 with a write gap WG therebetween.

[0048] As shown in FIGS. 4 to 7, the recording head 56 comprises a pair of
side shields 70 located individually on opposite sides of the main pole
66 along the length of the write gap GW, that is, transversely relative
to the track. The side shields 70 are magnetically separated from the
main pole 66 on the ABS 43. In the present embodiment, the side shields
70 are formed integrally with the distal end portion 68a of the return
pole 68 from a high-permeability material, and protrude from the leading
end face 68b of the distal end portion 68a toward the leading end of the
slider 42. Each side shield 70 extends from the leading end face 68b of
the return pole 68 to the same level as the leading end face 67b of the
main pole 66.

[0049] As shown in FIGS. 3 to 6, the second magnetic core 56b of the
recording head 56 comprises a first magnetic pole 72 of a
high-permeability material on the leading side of the main pole 66 and a
second magnetic pole 74 of a high-permeability material on the leading
side of the first magnetic pole. The first magnetic pole 72 comprises a
pair of first yoke portions 76, which are forked at its distal or
disk-side end portion. These first yoke portions 76 are connected to the
return pole 68, or in the present embodiment, to the side shields 70,
individually. The second magnetic pole 74 comprises a pair of second yoke
portions 78, which are forked at its distal or disk-side end portion.
These second yoke portions 78 are connected to the return pole 68, or in
this case, to the side shields 70, individually.

[0050] The respective upper end portions of the first and second magnetic
poles 72 and 74 are connected to each other by a junction 77 of a
high-permeability material. Thus, the second magnetic core 56b forms a
physically closed magnetic path, a part of which includes the return pole
68. A second coil 80 that excites magnetic flux in the closed path formed
by the second magnetic core 56b is arranged so as to wind around the
second magnetic core 56b. The second coil 80 may be connected in series
with the recording coil 71. Alternatively, these coils may be
independently subjected to current supply control. As described later,
currents supplied to the recording coil 71 and second coil 80 are
controlled by the control section of the HDD.

[0051] As shown in FIG. 3, a protective insulating film 82 entirely covers
the reproduction head 54 and recording head 56 except for those parts
which are exposed in the ABS 43 of the slider 42. The protective
insulating film 82 defines the contour of the head section 44.

[0052] When the VCM 15 is activated, according to the HDD constructed in
this manner, the head actuator 14 pivots, whereupon each magnetic head 33
is moved to and positioned on the desired track of the magnetic disk 12.
Further, the magnetic head 33 is caused to fly by airflow C that is
produced between the disk surface and the ABS 43 as the magnetic disk 12
rotates. When the HDD is operating, the ABS 43 of the slider 42 is
opposed to the disk surface with a gap therebetween. As shown in FIG. 2,
the magnetic head 33 is caused to fly with the recording head 56 of the
head section 44 inclined to be closest to the surface of the disk 12. In
this state, the reproduction head 54 reads recorded data from the disk
12, while the recording head 56 writes data to the disk.

[0053] In writing data, the recording coil 71 excites the main pole 66,
which applies a perpendicular recording magnetic field to the recording
layer 22 of the magnetic disk 12 just below the main pole, thereby
recording data with a desired track width. At the same time, as indicated
by the arrows in FIG. 6, a current is passed through the second coil 80
to excite the second magnetic core 56b so that a desired magnetic field
flows through the closed magnetic path including the side shields 70.

[0054] When this is done, the side shields 70 on the opposite sides of the
main pole 66 make it possible to suppress magnetic flux leakage from the
distal end portion 66a of the main pole 66 to adjacent tracks without
reducing the quality of signals to be written to a write track.
Concentration of a return magnetic field on the side shields 70 can be
prevented by passing the desired magnetic field through the second
magnetic core 56b that forms the closed magnetic path including the side
shields 70. Thus, a magnetic field from the main pole 66 applied to the
recording layer 22 is prevented from intensively returning toward the
side shields 70 by the magnetic field flowing through the closed magnetic
path including the side shields 70, as shown in FIG. 6. After the applied
magnetic field propagates through the underlayer 23 along its surface, it
gradually returns to the return pole.

[0055] Thus, recorded data in adjacent tracks off the write track can be
prevented from being degraded or erased. Accordingly, data erasure in the
adjacent tracks can be prevented while maintaining the recording capacity
in the write track. Consequently, the track density of the recording
layer of the magnetic disk 12 can be increased, so that the recording
density of the HDD can be increased.

[0056] FIG. 8 is a block diagram showing the control section for
controlling the currents supplied to the recording coil 71 and second
coil 80. For example, a control section 83 in the printed circuit board
25 of the HDD comprises first and second current controllers 84 and 85,
head position controller 86, error-rate measurement section 87, data
storage section 88, and data operation section 90. The first current
controller 84 sets a current Iw1 to be passed through the recording coil
71. The second current controller 85 sets a current Iw2 to be passed
through the second coil 80.

[0057] In setting currents Iw1 and Iw2, current Iw2 is first set by the
second current controller 85, and a random signal obtained by variously
changing current Iw1 by the first current controller 84 is then recorded
in the magnetic disk in a track position determined by the head position
controller 86. Thereafter, the recorded data is read by the magnetic
head, and an error rate is measured by the error-rate measurement section
87. After data is recorded ten thousand times in the magnetic disk in a
position at a certain pitch from an initial recording track position,
moreover, the error rate is measured again in the initial track position
and stored in the data storage section 88.

[0058] Further, currents Iw1 and Iw2 are individually changed as the track
pitch and error rate are measured and stored in the data storage section
88 in the same processes as aforesaid. Based on the data thus acquired,
the data operation unit 90 calculates a current with which a minimum
feasible track pitch to reduce the error rate is obtained. In this way,
optimum current Iw2 to be passed through the second coil 80 is
determined.

[0059] FIG. 9 shows fluctuations of the error rate obtained when current
Iw2 and the track pitch are changed. As seen from this diagram, the
relationship between the error rate and track pitch varies depending on
the magnitude of current Iw2. Specifically, as the error rate and track
pitch vary according to each current (Iw2-1, Iw2-2 or Iw2-3), a minimum
track pitch with which a desired error rate can be achieved is assumed to
be the track pitch that is realizable with current Iw2. In FIG. 8, Tp1,
Tp2 and Tp3 are minimum track pitches realizable with currents Iw2-1,
Iw2-2, and Iw2-1, respectively.

[0060] FIG. 10 shows the relationship between current Iw2 and realized
track pitch. According to the magnetic head of the present embodiment,
the track pitch can be reduced from Tp1 to Tp2 to increase the track
density by setting an Iw2 set magnitude for the minimum realized track
pitch by means of the current controller 85.

[0061] In connecting the recording coil 71 and second coil 80 in series,
magnetic fields produced in the first and second magnetic cores 56a and
56b can be controlled with a common current Iw by appropriately setting
the number of turns of each coil.

[0062] The inventor hereof prepared the magnetic head 33 according to the
present embodiment and a magnetic head according to a comparative example
and compared their respective bit error rates obtained during recording
and reproduction operations using them. The comparative example is a
magnetic head for perpendicular magnetic recording, which comprises a
main pole, return pole, and side shields, but not a second magnetic core.

[0063] FIG. 11 shows transverse distributions (relative to the track) of
magnetic fields produced from just below and from near the main pole with
the track center of the recording head assumed to be a position 0, for
each of the magnetic heads according to the present embodiment and
comparative example. In the magnetic head according to the comparative
example, as seen from FIG. 11, magnetic fields of opposite polarity to
that of a field in the central part of a main pole 66 are produced near
the respective end portions of side shields 70 on the main-pole side. In
the magnetic head 33 according to the present embodiment, there exist no
fringes of magnetic fields of the same polarity as that of the central
magnetic field, and no opposite-polarity magnetic fields are produced
either.

[0064] FIG. 12 is a diagram showing an error-rate measurement method for
each of the magnetic heads according to the present embodiment and
comparative example. FIG. 13 is a diagram showing measured error rate
track profiles for comparison. In measuring the error rate, random data
is recorded and reproduced for each shifting track pitch, as shown in
FIG. 12(a). Then, the random data is recorded ten thousand times along
the track center, as shown in FIG. 12(b). Thereafter, the error rate is
measured for each shifting track pitch, as shown in FIG. 12(c).
Consequently, as seen from FIG. 13, the error rate is degraded near the
end portion of each side shield on the main-pole side if the recording
head of the magnetic head according to the comparative example is placed
on the track center. The use of the magnetic head according to the
present embodiment does not result in any error rate degradation just
below the side shields. Thus, the recording head of the present
embodiment can accurately store recorded data for a long period of time.

[0065] According to the magnetic head of the present embodiment and the
HDD provided with the same, as described above, a return magnetic field
is not produced in the recording layer position just below the return
pole, and recorded data can be prevented from being degraded or erased at
a distant track position. There may be provided a magnetic head,
configured to prevent data erasure in adjacent tracks while maintaining
the recording capacity on a write track and increase the track density of
a recording layer of a magnetic disk, thereby increasing the recording
density, and a disk drive provided with the same.

[0066] The following is a description of a magnetic head of an HDD
according to a second embodiment.

[0067] The magnetic head of the second embodiment differs from that of the
first embodiment mainly in the configurations of the side shields and
second magnetic core, and other configurations are the same as those of
the magnetic head of the first embodiment. Therefore, like reference
numbers refer to like portions of these two embodiments, and a detailed
description of those portions is omitted.

[0068] FIG. 14 is an exemplary exploded perspective view schematically
showing a recording head 56 of the magnetic head of the HDD according to
the second embodiment, FIG. 15 is an exemplary side view schematically
showing the recording head, and FIG. 16 is an exemplary plan view of the
recording head taken from the side of an ABS.

[0069] According to the second embodiment, a first magnetic core 56a of
the recording head 56 comprises a main pole 66 and return pole 68. A pair
of side shields 70 located individually on opposite sides of the main
pole 66 transversely relative to the track are formed integrally with the
return pole 68 and protrude from a leading end face 68b of the return
pole 68. The side shields 70 are magnetically separated from the main
pole 66 on the ABS. A leading end portion of each side shield 70 projects
beyond a leading end face 67b of a distal end portion 66a of the main
pole 66 to the leading side. Respective extended ends of the side shields
70 are connected to each other by a junction 92. The junction 92 faces
the leading end face 67b of the distal end portion 66a of the main pole
66 with a predetermined gap therebetween.

[0070] A second magnetic core 56b of the recording head 56 comprises a
first magnetic pole 72 of a high-permeability material on the leading
side of the main pole 66 and a second magnetic pole 74 of a
high-permeability material on the leading side of the first magnetic
pole. The first magnetic pole 72 comprises a first yoke portion 76 on its
distal or disk-side end portion. The first yoke portion 76 is connected
to the junction 92 between the side shields 70. The second magnetic pole
74 comprises a second yoke portion 78 integrally formed on its distal end
portion. The second yoke portion 78 is connected to the junction 92
between the side shields 70.

[0071] The respective upper end portions of the first and second magnetic
poles 72 and 74 are connected to each other by a junction 77 of a
high-permeability material. Thus, the second magnetic core 56b forms a
physically closed magnetic path, a part of which includes the side
shields 70. A second coil 80 that excites magnetic flux in the closed
path formed by the second magnetic core 56b is arranged so as to wind
around the second magnetic core 56b. The second coil 80 may be connected
in series with a recording coil 71. Alternatively, these coils may be
independently subjected to current supply control. As in the first
embodiment, currents supplied to the recording coil 71 and second coil 80
are controlled by a control section of the HDD.

[0072] In writing data, according to the magnetic head and HDD of the
second embodiment constructed in this manner, the recording coil 71
excites the main pole 66 to apply a perpendicular recording magnetic
field to a recording layer 22 of a magnetic disk 12 just below the main
pole, thereby recording data with a desired track width. At the same
time, a current is passed through the second coil 80 to excite the second
magnetic core 56b so that a desired magnetic field flows through the
closed magnetic path including the side shields 70.

[0073] When this is done, the side shields 70 on the opposite sides of the
main pole 66 make it possible to suppress magnetic flux leakage from the
distal end portion 66a of the main pole 66 to adjacent tracks without
reducing the quality of signals to be written to a write track. Since the
side shields 70 are provided with the junction 92 on the leading side of
the main pole 66, moreover, magnetic flux leakage to adjacent tracks can
be further suppressed. Concentration of a return magnetic field on the
side shields 70 can be prevented by passing the desired magnetic field
through the second magnetic core 56b that forms the closed magnetic path
including the side shields 70. Thus, a magnetic field from the main pole
66 applied to the recording layer 22 is prevented from intensively
returning toward the side shields 70 by the magnetic field flowing
through the closed magnetic path including the side shields 70. After the
applied magnetic field propagates through the underlayer 23 along its
surface, it gradually returns to the return pole.

[0074] Thus, recorded data in adjacent tracks off the write track can be
prevented from being degraded or erased. Accordingly, data erasure in the
adjacent tracks can be prevented while maintaining the recording capacity
on the write track. Consequently, the track density of the recording
layer of the magnetic disk can be increased, so that the recording
density of the HDD can be increased.

[0075] While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to limit
the scope of the inventions. Indeed, the novel embodiments described
herein may be embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the embodiments
described herein may be made without departing from the spirit of the
inventions. The accompanying claims and their equivalents are intended to
cover such forms or modifications as would fall within the scope and
spirit of the inventions.

[0076] For example, the materials, shapes, sizes, etc., of the constituent
elements of the head section may be changed if necessary. Further, the
number of magnetic disks and heads used in the magnetic disk drive may be
increased as required, and the size of each magnetic disk can be
variously selected.

Patent applications by Tomoko Taguchi, Kunitachi-Shi JP

Patent applications by KABUSHIKI KAISHA TOSHIBA

Patent applications in class GENERAL PROCESSING OF A DIGITAL SIGNAL

Patent applications in all subclasses GENERAL PROCESSING OF A DIGITAL SIGNAL